Impulse-Based Compact Mechanical G-Switch With Modular Design

ABSTRACT

A G-switch including: a base and posts, the posts having a hole; a locking ball with a portion disposed in the holes; a striker mass movably disposed relative to the posts and having a concave portion, wherein a portion of the locking balls is disposed the concave portion; a collar movable relative to the posts; a biasing element for biasing the collar in a position which retains the locking balls within the concave portions, the biasing element permitting movement of the collar to a position in which the locking balls are released from the concave portions to release the striker mass upon a predetermined acceleration profile; and a member on the striker mass and first and second electrically conductive contacts on a portion of the body, the first member opening or closing an electrical circuit between the first and second contacts upon release of the striker mass.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.12/835,709 filed on Jul. 13, 2010, now U.S. Application PublicationNumber 2011/0171511, which claims the benefit of U.S. ProvisionalApplication No. 61/239,048 filed on Sep. 1, 2009, the entire contents ofeach of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to mechanical G-switches, andmore particularly to compact, low-volume, reliable and easy tomanufacture mechanical G-switches that are impulse-based and activatethe switching action to open and/or close at least one electricalcircuit or the like igniters when it is subjected to a prescribedacceleration level acting over prescribed time duration.

2. Prior Art

Thermal batteries represent a class of reserve batteries that operate athigh temperature. Unlike liquid reserve batteries, in thermal batteriesthe electrolyte is already in the cells and therefore does not require adistribution mechanism such as spinning. The electrolyte is dry, solidand non-conductive, thereby leaving the battery in a non-operational andinert condition. These batteries incorporate pyrotechnic heat sources tomelt the electrolyte just prior to use in order to make themelectrically conductive and thereby making the battery active. The mostcommon internal pyrotechnic is a blend of Fe and KClO₄. Thermalbatteries utilize a molten salt to serve as the electrolyte uponactivation. The electrolytes are usually mixtures of alkali-halide saltsand are used with the Li(Si)/FeS₂ or Li(Si)/CoS₂ couples. Some batteriesalso employ anodes of Li(Al) in place of the Li(Si) anodes. Insulationand internal heat sinks are used to maintain the electrolyte in itsmolten and conductive condition during the time of use. Reservebatteries are inactive and inert when manufactured and become active andbegin to produce power only when they are activated.

Thermal batteries have long been used in munitions and other similarapplications to provide a relatively large amount of power during arelatively short period of time, mainly during the munitions flight.Thermal batteries have high power density and can provide a large amountof power as long as the electrolyte of the thermal battery stays liquid,thereby conductive. The process of manufacturing thermal batteries ishighly labor intensive and requires relatively expensive facilities.Fabrication usually involves costly batch processes, including pressingelectrodes and electrolytes into rigid wafers, and assembling batteriesby hand. The batteries are encased in a hermetically-sealed metalcontainer that is usually cylindrical in shape. Thermal batteries,however, have the advantage of very long shelf life of up to 20 yearsthat is required for munitions applications.

Thermal batteries generally use some type of igniter to provide acontrolled pyrotechnic reaction to produce output gas, flame or hotparticles to ignite the heating elements of the thermal battery. Thereare currently two distinct classes of igniters that are available foruse in thermal batteries. The first class of igniter operates based onelectrical energy. Such electrical igniters, however, require electricalenergy, thereby requiring an onboard battery or other power sources withrelated shelf life and/or complexity and volume requirements to operateand initiate the thermal battery. The second class of igniters, commonlycalled “inertial igniters”, operates based on the firing acceleration.The inertial igniters do not require onboard batteries for theiroperation and are thereby often used in high-G munitions applicationssuch as in gun-fired munitions and mortars.

In general, the inertial igniters, particularly those that are designedto operate at relatively low impact levels, have to be provided with themeans for distinguishing events such as accidental drops or explosionsin their vicinity from the firing acceleration levels above which theyare designed to be activated. This means that safety in terms ofprevention of accidental ignition is one of the main concerns ininertial igniters.

In recent years, new improved chemistries and manufacturing processeshave been developed that promise the development of lower cost andhigher performance thermal batteries that could be produced in variousshapes and sizes, including their small and miniaturized versions.However, the existing inertial igniters are relatively large and notsuitable for small and low power thermal batteries, particularly thosethat are being developed for use in miniaturized fuzing, future smartmunitions, and other similar applications.

The need to differentiate accidental and initiation accelerations by theresulting impulse level of the event necessitates the employment of asafety system which is capable of allowing initiation of the igniteronly during high total impulse levels. The safety mechanism can bethought of as a mechanical delay mechanism, after which a separateinitiation system is actuated or released to provide ignition of thepyrotechnics. An inertial igniter that combines such a safety systemwith an impact based initiation system and its alternative embodimentsare described herein together with alternative methods of initiationpyrotechnics.

Inertia-based igniters must therefore comprise two components so thattogether they provide the aforementioned mechanical safety (delaymechanism) and to provide the required striking action to achieveignition of the pyrotechnic elements. The function of the safety systemis to fix the striker in position until a specified acceleration timeprofile actuates the safety system and releases the striker, allowing itto accelerate toward its target under the influence of the remainingportion of the specified acceleration time profile. The ignition itselfmay take place as a result of striker impact, or simply contact orproximity. For example, the striker may be akin to a firing pin and thetarget akin to a standard percussion cap primer. Alternately, thestriker-target pair may bring together one or more chemical compoundswhose combination with or without impact will set off a reactionresulting in the desired ignition.

In addition to having a required acceleration time profile which willactuate the device, requirements also commonly exist for non-actuationand survivability. For example, the design requirements for actuationfor one application are summarized as:

1. The device must fire when given a [square] pulse acceleration of 900G±150 G for 15 ms in the setback direction.

2. The device must not fire when given a [square] pulse acceleration of2000 G for 0.5 ms in any direction.

3. The device must not actuate when given a ½-sine pulse acceleration of490 G (peak) with a maximum duration of 4 ms.

4. The device must be able to survive an acceleration of 16,000 G, andpreferably be able to survive an acceleration of 50,000 G.

A schematic of a cross-section of a conventional thermal battery andinertial igniter assembly is shown in FIG. 1. In thermal batteryapplications, the inertial igniter 10 (as assembled in a housing) isgenerally positioned above the thermal battery housing 11 as shown inFIG. 1. Upon ignition, the igniter initiates the thermal batterypyrotechnics positioned inside the thermal battery through a providedaccess 12. The total volume that the thermal battery assembly 16occupies within munitions is determined by the diameter 17 of thethermal battery housing 11 (assuming it is cylindrical) and the totalheight 15 of the thermal battery assembly 16.

The height 14 of the thermal battery for a given battery diameter 17 isgenerally determined by the amount of energy that it has to produce overthe required period of time. For a given thermal battery height 14, theheight 13 of the inertial igniter 10 would therefore determine the totalheight 15 of the thermal battery assembly 16. To reduce the total volumethat the thermal battery assembly 16 occupies within a munitionshousing, it is therefore important to reduce the height of the inertialigniter 10. This is particularly important for small thermal batteriessince in such cases the inertial igniter height with currently availableinertial igniters can be almost the same order of magnitude as thethermal battery height.

With currently available inertial igniters, a schematic of which isshown in FIG. 2, the inertial igniter 20 may have to be positionedwithin a housing 21 as shown in FIG. 3, particularly for relativelysmall igniters. The housing 21 and the thermal battery housing 11 mayshare a common cap 22, with the opening 25 to allow the ignition fire toreach the pyrotechnic material 24 within the thermal battery housing. Asthe inertial igniter is initiated, the sparks can ignite intermediatematerials 23, which can be in the form of thin sheets to allow for easyignition, which would in turn ignite the pyrotechnic materials 24 withinthe thermal battery through the access hole 25.

A schematic of a cross-section of a currently available inertial igniter20 is shown in FIG. 2 in which the acceleration is in the upwarddirection (i.e., towards the top of the paper). The igniter has sideholes 26 to allow the ignition fire to reach the intermediate materials23 as shown in FIG. 3, which necessitate the need for its packaging in aseparate housing, such as in the housing 21. The currently availableinertial igniter 20 is constructed with an igniter body 60. Attached tothe base 61 of the housing 60 is a cup 62, which contains one part of atwo-part pyrotechnic compound 63 (e.g., potassium chlorate). The housing60 is provided with the side holes 26 to allow the ignition fire toreach the intermediate materials 23 as shown in FIG. 3. A cylindricalshaped part 64, which is free to translate along the length of thehousing 60, is positioned inside the housing 60 and is biased to stay inthe top portion of the housing as shown in FIG. 2 by the compressivelypreloaded helical spring 65 (shown schematically as a heavy line). Aturned part 71 is firmly attached to the lower portion of thecylindrical part 64. The tip 72 of the turned part 71 is provided withcut rings 72a, over which is covered with the second part of thetwo-part pyrotechnic compound 73 (e.g., red phosphorous).

A safety component 66, which is biased to stay in its upper mostposition as shown in FIG. 2 by the safety spring 67 (shown schematicallyas a heavy line), is positioned inside the cylinder 64, and is free tomove up and down (axially) in the cylinder 64. As can be observed inFIG. 2, the cylindrical part 64 is locked to the housing 60 by setbacklocking balls 68. The setback locking balls 68 lock the cylindrical part64 to the housing 60 through holes 69 a provided on the cylindrical part64 and the housing 60 and corresponding holes 69 b on the housing 60. Inthe illustrated configuration, the safety component 66 is pressing thelocking balls 68 against the cylindrical part 64 via the preloadedsafety spring 67, and the flat portion 70 of the safety component 66prevents the locking balls 68 from moving away from their aforementionedlocking position. The flat portion 70 of the safety component 66 allowsa certain amount of downward movement of the safety component 66 withoutreleasing the locking balls 68 and thereby allowing downward movement ofthe cylindrical part 64. For relatively low axial acceleration levels orhigher acceleration levels that last a very short amount of time,corresponding to accidental drops and other similar situations thatcause safety concerns, the safety component 66 travels up and downwithout releasing the cylindrical part 64. However, once the firingacceleration profiles are experienced, the safety component 66 travelsdownward enough to release balls 68 from the holes 69 b and therebyrelease the cylindrical part 64. Upon the release of the safetycomponent 66 and appropriate level of acceleration for the cylindricalpart 64 and all other components that ride with it to overcome theresisting force of the spring 65 and attain enough momentum, then itwill cause impact between the two components 63 and 73 of the two-partpyrotechnic compound with enough strength to cause ignition of thepyrotechnic compound.

The aforementioned currently available inertial igniters have a numberof shortcomings for use in thermal batteries, specifically, they are notuseful for relatively small thermal batteries for munitions with the aimof occupying relatively small volumes, i.e., to achieve relatively smallheight total igniter compartment height 13, FIG. 1. Firstly, thecurrently available inertial igniters, such as that shown in FIG. 2, arerelatively long thereby resulting in relatively long total igniterheights 13. Secondly, since the currently available igniters are notsealed and exhaust the ignition fire out from the sides, they have to bepackaged in a housing 21, usually with other ignition material 23,thereby increasing the height 13 over the length of the igniter 20 (seeFIG. 3). In addition, since the pyrotechnic materials of the currentlyavailable igniters 20 are not sealed inside the igniter, they are proneto damage by the elements and cannot usually be stored for long periodsof time before assembly into the thermal batteries unless they arestored in a controlled environment.

It is also appreciated by those skilled in the art that currentlyavailable G-switches of different type that are used for opening orclosing an electrical circuit are designed to perform this function whenthey are subjected to a prescribed acceleration level without accountingfor the duration of the said acceleration level. As such, they sufferfrom the shortcoming of being activated accidentally, e.g., when theobject in which they are used is subjected to short duration shockloading such as could be experienced when dropped on a hard surface aswas previously described for the case of inertial igniter used inmunitions.

When used in applications such as in munitions, it is highly desirablefor G-switches to be capable to differentiate the aforementionedaccidental and short duration shock (acceleration) events such as thoseexperienced by dropping on hard surfaces, i.e., all no-fire conditions,from relatively longer duration firing setback (shock) accelerations,i.e., the all-fire condition. Such G-switches should activate whenfiring setback (all-fire) acceleration and its duration results in animpulse level threshold corresponding to the all-fire event to bereached. This requirement necessitates the employment of safetymechanisms similar to those used in the aforementioned inertial igniterembodiments which are capable of allowing the G-switch activation onlywhen the high total firing setback impulse level threshold has beenreached. The safety mechanism can be thought of as a mechanical delaymechanism, after which a separate G-switch mechanism is actuated orreleased to provide the means of opening or closing at least oneelectrical circuit. Such G-switch embodiments that combine such safetymechanisms with electrical switching mechanisms are described hereintogether with alternative methods of their construction.

Such G-switches with the aforementioned integrated safety mechanisms arehighly desirable to be very small in size so that they could be readilyused on electronic circuit boards of different products such asmunitions or the like.

SUMMARY OF THE INVENTION

A need therefore exists for novel miniature inertial igniters forthermal batteries used in gun fired munitions, particularly for smalland low power thermal batteries that could be used in fuzing and othersimilar applications, thereby eliminating the need for external powersources. The innovative inertial igniters can be scalable to thermalbatteries of various sizes, in particular to miniaturized igniters forsmall size thermal batteries. Such inertial igniters must be safe and ingeneral and in particular they should not initiate if dropped, e.g.,from up to 7 feet onto a concrete floor for certain applications; shouldwithstand high firing accelerations, for example up to 20-50,000 Gs; andshould be able to be designed to ignite at specified acceleration levelswhen subjected to such accelerations for a specified amount of time tomatch the firing acceleration experienced in a gun barrel as compared tohigh G accelerations experienced during accidental falls which last oververy short periods of time, for example accelerations of the order of1000 Gs when applied for 5 msec as experienced in a gun as compared tofor example 2000 G acceleration levels experienced during accidentalfall over a concrete floor but which may last only 0.5 msec. Reliabilityis also of much concern since the rounds should have a shelf life of upto 20 years and could generally be stored at temperatures of sometimesin the range of −65 to 165 degrees F. This requirement is usuallysatisfied best if the igniter pyrotechnic is in a sealed compartment.The inertial igniters must also consider the manufacturing costs andsimplicity in design to make them cost effective for munitionsapplications.

To ensure safety and reliability, inertial igniters should not initiateduring acceleration events which may occur during manufacture, assembly,handling, transport, accidental drops, etc. Additionally, once under theinfluence of an acceleration profile particular to the firing ofordinance from a gun, the device should initiate with high reliability.In many applications, these two requirements often compete with respectto acceleration magnitude, but differ greatly in impulse. For example,an accidental drop may well cause very high acceleration levels—even insome cases higher than the firing of a shell from a gun. However, theduration of this accidental acceleration will be short, therebysubjecting the inertial igniter to significantly lower resulting impulselevels. It is also conceivable that the igniter will experienceincidental low but long-duration accelerations, whether accidental or aspart of normal handling, which must be guarded against initiation.Again, the impulse given to the miniature inertial igniter will have agreat disparity with that given by the initiation acceleration profilebecause the magnitude of the incidental long-duration acceleration willbe quite low.

Those skilled in the art will appreciate that the inertial ignitersdisclosed herein may provide one or more of the following advantagesover prior art inertial igniters:

provide inertial igniters that are significantly shorter and smaller involume than currently available inertial igniters for thermal batteriesor the like, particularly relatively small thermal batteries to be usedin munitions without occupying very large volumes;

provide inertial igniters that can be mounted directly onto the thermalbatteries without a housing (such as housing 21 shown in FIG. 3),thereby allowing even a smaller total height and volume for the inertialigniter assembly;

provide inertial igniters that can directly initiate the pyrotechnicsmaterials inside the thermal battery without the need for intermediateignition material (such as the additional material 23 shown in FIG. 3)or a booster;

provide inertia igniters that could be constructed to guide thepyrotechnic flame essentially downward (in the direction opposite to thedirection of the firing acceleration—usually for mounting on the top ofthe thermal battery as shown in FIG. 3), or essentially upward (in thedirection opposite of the firing acceleration—usually for mounting atthe bottom of the thermal battery), or essentially sidewise (lateral tothe direction of the firing);

provide inertial igniters that allow the use of standard off-the-shelfpercussion cap primers instead of specially designed pyrotechniccomponents; and

provide inertial igniters that can be sealed to simplify storage andincrease their shelf life.

Accordingly, inertial igniters and ignition systems for use with thermalbatteries for producing power upon acceleration are provided.

A need therefore exists for novel miniature G-switches for use inmunitions or the like that can differentiate accidental short durationshock loading (so-called no-fire events for munitions) from generallyhigh but longer duration, i.e., high impulse threshold levels, thatcorrespond to all-fire conditions in gun fired munitions or the like.Such G-switches must be very small in size and volume to make themsuitable for being integrated into electronic circuit boards or thelike. They must also be readily scalable to different all-fire andno-fire conditions for different munitions or other similarapplications. Such G-switches must be safe and in general and inparticular they should not activate if dropped, e.g., from up to 7 feetonto a concrete floor for certain applications; should withstand highfiring accelerations, for example up to 20-50,000 Gs and sometimeshigher; and should be able to be designed to activate at specifiedacceleration levels when subjected to such accelerations for a specifiedamount of time to match the firing acceleration experienced in a gunbarrel as compared to high G accelerations experienced during accidentalfalls or other similar events which last over very short periods oftime, for example accelerations of the order of 1000 Gs when applied for5 msec as experienced in a gun as compared to for example 2000 Gacceleration levels experienced during accidental fall over a concretefloor but which may last only 0.5 msec. Reliability is also of muchconcern since most munitions are required to have a shelf life of up to20 years and could generally be stored at temperatures of sometimes inthe range of −65 to 165 degrees F. This requirement is usually satisfiedbest if the device is in a sealed compartment. The G-switch must alsoconsider the manufacturing costs and simplicity of design to make themcost effective for munitions applications.

Those skilled in the art will appreciate that the compact impulse-basedmechanical G-switches disclosed herein may provide one or more of thefollowing advantages over prior art mechanical G-switches:

provide impulse-based G-switches that are small in both height andvolume, thereby making tem suitable for mounting directly on electroniccircuit boards and the like;

provide impulse-based G-switches that differentiate all-fire conditionsfrom all no-fire conditions, even those no-fire conditions that resultin higher levels of shock; accelerations but have short duration,thereby eliminating the possibility of accidental activation;

provide G-switches that are modular in design and can therefore bereadily customized to different no-fire and all-fire requirements;

provide G-switches that may be normally open or normally closed and thatare modular in design and can be readily customized for opening orclosing or their combination of at least one electric circuit.

Accordingly, impulse-based G-switches with modular design for use inelectrical or electronic circuitry are provided that activate upon aprescribed acceleration profile threshold. In most munitionsapplications, the acceleration profile is usually defined in terms offiring setback acceleration and its duration.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the apparatus ofthe present invention will become better understood with regard to thefollowing description, appended claims, and accompanying drawings where:

FIG. 1 illustrates a schematic of a cross-section of a thermal batteryand inertial igniter assembly.

FIG. 2 illustrates a schematic of a cross-section of a conventionalinertial igniter assembly known in the art.

FIG. 3 illustrates a schematic of a cross-section of a conventionalinertial igniter assembly known in the art positioned within a housingand having intermediate materials for ignition.

FIG. 4 illustrates a schematic of a cross-section of a first embodimentof an inertial igniter in a locked position.

FIG. 5 a illustrates a schematic of the isometric drawing of a firstembodiment of an inertial igniter together with the top cap of a thermalbattery to which it is attached.

FIG. 5 b illustrates a second view of the isometric drawing of the firstembodiment of the inertial igniter of FIG. 5 a showing the openings thatare provided to exit the ignition sparks and flames into the thermalbattery.

FIG. 5 c illustrates a schematic of the isometric drawing of a firstembodiment of an inertial igniter of FIG. 5 a without the outer housing(side wall and top cap) of the inertial igniter.

FIG. 6 illustrates the inertial igniter of FIG. 4 upon a non-firingaccidental acceleration.

FIG. 7 illustrates the inertial igniter of FIG. 4 upon a firingacceleration.

FIG. 8 illustrates the inertial igniter of FIG. 4 upon the striker massimpacting base, causing the initiation of ignition of the two-partpyrotechnic compound.

FIG. 9 illustrates a schematic of a cross-section of a second embodimentof an inertial igniter in a locked position.

FIG. 10 illustrates a schematic of a cross-section of a third embodimentof an inertial igniter in initiation position.

FIGS. 11 a and 11 b illustrate an isometric and a schematic of across-section, respectively, of a fourth embodiment of an inertialigniter in initiation position.

FIG. 12 illustrates a schematic of a cross-section of a fifth embodimentof an inertial igniter in a locked position.

FIG. 13 illustrates an isometric cut away view of a sixth embodiment ofan inertial igniter.

FIG. 14 illustrates a full isometric view of the inertial igniter ofFIG. 13.

FIGS. 15 a and 15 b illustrate first and second variations of thermalbattery and inertial igniter assemblies.

FIG. 16 illustrates a first variation of the inertial igniter of FIG.13.

FIG. 17 illustrates a second variation of the inertial igniter of FIG.13.

FIG. 18 illustrates a third variation of the inertial igniter of FIG.13.

FIG. 19 illustrates a thermal battery/inertial igniter assembly in whichmore than one inertial igniter is used.

FIG. 20 a illustrates a top view and FIGS. 20 b illustrates an isometricview of a bottom plate and posts for a gang of three inertial igniters.

FIG. 21 a illustrates a top view and FIGS. 21 b illustrates an isometricview of a bottom plate and posts for a variation of the gang of threeinertial igniters of FIGS. 20 a and 20 b.

FIG. 22 illustrates a schematic of the first embodiment of animpulse-based G-switch for closing electrical circuits when subjected toa prescribed all-fire or the like condition.

FIG. 23 illustrates the schematic of the second embodiment of animpulse-based G-switch embodiment for closing electrical circuits whensubjected to a prescribed all-fire or the like condition and with aswitching contact preserving preloaded compressive spring.

FIG. 24 illustrates a schematic of the third embodiment of animpulse-based G-switch for opening electrical circuit when subjected toa prescribed all-fire or the like condition.

FIG. 25 illustrates the schematic of the fourth embodiment of animpulse-based G-switch embodiment for opening electrical circuits whensubjected to a prescribed all-fire or the like condition.

FIG. 26 illustrates the schematic of the fifth embodiment of animpulse-based G-switch embodiment for closing electrical circuits whensubjected to a prescribed all-fire or the like condition.

FIG. 27 illustrates the schematic of an integrated member that can beused to simplify the construction of certain embodiments of thedisclosed G-switched.

FIG. 28 illustrates the schematic of an integrated member that can beused to simplify the construction of certain other embodiments of thedisclosed G-switched.

FIG. 29 illustrates the schematic of an integrated member that can beused to simplify the construction of certain other embodiments of thedisclosed G-switched.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A schematic of a cross-section of a first embodiment of an inertiaigniter is shown in FIG. 4, referred to generally with reference numeral30. The inertial igniter 30 is constructed with igniter body 31,consisting of a base 32 and at least two posts 33, and a housing wall34. The base 32 and two posts 33, which may be integral or may have beenconstructed as separate pieces and joined together, for example bywelding of press fitting or other methods commonly used in the art. Inthe schematic of FIG. 4, the igniter body 31 and the housing wall 34 areshown to be joined together at the base 32; however, the two componentsmay be integrated as one piece and a separate top cap 35 may then beprovided, which is then joined to the top surface of the housing 34following assembly of the igniter (in the schematic of FIG. 4 the topcap 35 is shown as an integral part of the housing 34). In addition, thebase of the housing 32 may be extended to form the cap 36 of the thermalbattery 37, the top portion of which is shown with dashed lines in FIG.4.

The inertial igniter 30 with the thermal battery top cap 36 is shown inthe isometric drawings of FIGS. 5 a and 5 b. The inertial igniterwithout its housing 34 and top cap 35 is shown in the isometric drawingof FIG. 5 c. The base of the housing 32 is also provided with at leastone opening 38 (with corresponding openings in the thermal battery topcap 36) to allow the ignited sparks and fire to exit the inertialigniter into the thermal battery 37 upon initiation of the inertialigniter pyrotechnics 46 and 47, FIG. 4, or percussion cap primer whenused in place of the pyrotechnics 46 and 47 (not shown).

A striker mass 39 is shown in its locked position in FIGS. 4 and 5 c.The striker mass 39 is provided with vertical recesses 40 that are usedto engage the posts 33 and serve as guides to allow the striker mass 39to ride down along the length of the posts 33 without rotation with anessentially pure up and down translational motion. In its illustratedposition in FIGS. 4 and 5 c, the striker mass 39 is locked in its axialposition to the posts 33 by at least one setback locking ball 42. Thesetback locking ball 42 locks the striker mass 39 to the posts 33 of theinertial igniter body 31 through the holes 41 provided in the posts 33and a concave portion such as a dimple (or groove) 43 on the strikermass 39 as shown in FIG. 4. A setback spring 44 with essentially deadcoil section 45, which is preferably in compression, is also providedaround but close to the posts as shown in FIGS. 4 and 5 c. In theconfiguration shown in FIG. 4, the locking balls 42 are prevented frommoving away from their aforementioned locking position by the dead coilsection 45 of the setback spring 44. The dead coil section 45 can rideup and down beyond the posts 33 as shown in FIGS. 4 and 5 c, but isbiased to stay in its upper most position as shown in the schematic ofFIG. 4 by the setback spring 44.

In this embodiment, a two-part pyrotechnics compound is shown to beused, FIG. 4. One part of the two-part pyrotechnics compound 47 (e.g.,potassium chlorate) is provided on the interior side of the base 32,preferably in a provided recess (not shown) over the exit holes 38. Thesecond part of the pyrotechnics compound (e.g., red phosphorous) 46 isprovided on the lower surface of the striker mass surface 39 facing thefirst part of the pyrotechnics compound 47 as shown in FIG. 4. Thesurfaces to which the pyrotechnic parts 46 and 47 are attached areroughened and/or provided with surface cuts, recesses, or the like ascommonly used in the art (not shown) to ensure secure attachment of thepyrotechnics materials to the applied surfaces.

In general, various combinations of pyrotechnic materials may be usedfor this purpose. One commonly used pyrotechnic material consists of redphosphorous or nano-aluminum, indicated as element 46 in FIG. 4, and isused with an appropriate binder (such as vinyl alcohol acetate resin ornitrocellulose) to firmly adhere to the bottom surface of the strikermass 39. The second component can be potassium chlorate, potassiumnitrate, or potassium perchlorate, indicated as element 47 in FIG. 4,and is used with a binder (preferably but not limited to with such asvinyl alcohol acetate resin or nitrocellulose) to firmly attach thecompound to the surface of the base 32 (preferably inside of a recessprovided in the base 32—not shown) as shown in FIG. 4.

The basic operation of the disclosed inertial igniter 30 will now bedescribed with reference to FIGS. 4-8. Any non-trivial acceleration inthe axial direction 48 which can cause dead coil section 45 to overcomethe resisting force of the setback spring 44 will initiate and sustainsome downward motion of only the dead coil section 45. The force due tothe acceleration on the striker mass 39 is supported at the dimples 43by the locking balls 42 which are constrained inside the holes 41 in theposts 33. If an acceleration time in the axial direction 48 imparts asufficient impulse to the dead coil section 45 (i.e., if an accelerationtime profile is greater than a predetermined threshold), it willtranslate down along the axis of the assembly until the setback lockingballs 42 are no longer constrained to engage the striker mass 39 to theposts 33 of the housing 31. If the acceleration event is not sufficientto provide this motion (i.e., the acceleration time profile providesless impulse than the predetermined threshold), the dead coil section 45will return to its start (top) position under the force of the setbackspring 44. The schematic of the inertial igniter 30 with the dead coilsection 45 moved down certain distance d1 as a result of an accelerationevent, which is not sufficient to unlock the striker mass 39 from theposts 33 of the housing 31, is shown in FIG. 6.

Assuming that the acceleration time profile was at or above thespecified “all-fire” profile, the dead coil section 45 will havetranslated down full-stroke d2, allowing the striker mass 39 toaccelerate down towards the base 32. In such a situation, since thelocking balls 42 are no longer constrained by the dead coil section 45,the downward force that the striker mass 39 has been exerting on thelocking balls 42 will force the locking balls 42 to move outward in theradial direction. Once the locking balls 42 are out of the way of thedimples 43, the downward motion of the striker mass 39 is no longerimpeded. As a result, the striker mass 39 moves downward, causing theparts 46 and 47 of the two-part pyrotechnic compound to strike with therequisite energy to initiate ignition. The configuration of the inertialigniter 30 when the balls 42 are free to move outward in the radialdirection, thereby releasing the striker mass 39 is shown in theschematic of FIG. 7. The configuration of the inertial igniter 30 whenthe part 46 of the two-part pyrotechnic compound is striking the part 47is shown in the schematic of FIG. 8.

In another embodiment, the dead coil section 45 may be constructed as aseparate collar and positioned similarly over the setback spring 44. Thecollar replacing the dead coil section 45 may also be attached to thetop coil of the setback spring 44, e.g., by welding, brazing, oradhesives such as epoxy, or the like. The advantage of attaching thecollar to the top of the setback spring 44 is that it would help preventit to get struck over the posts 33 as it is being pushed down by theapplied acceleration in the direction of the arrow 48, FIGS. 6-8.

Alternatively, the dead coil section 45 and the setback spring 44 may beintegral, made out of, for example, a cylindrical section with spiral orother type shaped cuts over its lower section to provide the requiredaxial flexibility to serve the function of the setback spring 44. Theupper portion of this cylinder is preferably left intact to serve thefunction of the dead coil section 45, FIGS. 6-8.

It is appreciated by those skilled in the art that by varying the massof the striker 39, the mass of the dead coil section 45, the spring rateof the setback spring 44, the distance that the dead coil section 45 hasto travel downward to release the locking balls 42 and thereby releasethe striker mass 39, and the distance between the parts 46 and 47 of thetwo-part pyrotechnic compound, the designer of the disclosed inertialigniter 30 can match the fire and no-fire impulse level requirements forvarious applications as well as the safety (delay or dwell action)protection against accidental dropping of the inertial igniter and/orthe munitions or the like within which it is assembled.

Briefly, the safety system parameters, i.e., the mass of the dead coilsection 45, the spring rate of the setback spring 44 and the dwellstroke (the distance that the dead coil section 44 has to traveldownward to release the locking balls 42 and thereby release the strikermass 39) must be tuned to provide the required actuation performancecharacteristics. Similarly, to provide the requisite impact energy, themass of the striker 39 and the separation distance between the parts 46and 47 of the two-part pyrotechnic compound must work together toprovide the specified impact energy to initiate the pyrotechnic compoundwhen subjected to the remaining portion of the prescribed initiationacceleration profile after the safety system has been actuated.

In addition, since the safety and striker systems each require a certainactuation distance to achieve the necessary performance, the mostaxially compact design is realized by nesting the two systems inparallel as it is done in the embodiment of FIG. 4. It is this nestingof the two safety and striker systems that allows the height of thedisclosed inertial igniter to be significantly shorter than thecurrently available inertial igniter design (as shown in FIG. 2), inwhich the safety and striker systems are configured in series. In fact,an initial prototype of the disclosed inertial igniter 30 has beendesigned to the fire and no-fire and safety specifications of thecurrently available inertial igniter shown in FIG. 2 and has achievedheight and volume reductions of over 60 percent. It is noted that byoptimizing the parameters of the disclosed inertial igniter, both heightand volume can be further reduced.

In another embodiment, the two-part pyrotechnics 46 and 47, FIG. 4, arereplaced by a percussion cap primer 49 attached to the base 32 of theinertial igniter 60 and a striker tip 50 as shown in the schematic of across-section of FIG. 9. In this illustration, all components are thesame as those shown in FIG. 4 with the exception of replacing thepercussion cap primer 49 and the striker tip 50 with striker assembly.The striker tip 50 is firmly attached to the striker mass 39.

The striker mass 39 and striker tip 50 may be a monolithic design withthe striking tip 50 being a machined boss protruding from the strikermass, or the striker tip 50 may be a separate piece pressed or otherwisepermanently fixed to the striker mass. A two-piece design would befavorable to the need for a striker whose density is different thansteel, but whose tip would remain hard and tough by attaching a steelball, hemisphere, or other shape to the striker mass. A monolithicdesign, however, would be generally favorable to manufacturing becauseof the reduction of part quantity and assembly operations.

An advantage of using the two component pyrotechnic materials as shownin FIG. 4 is that these materials can be selected such that ignition isprovided at significantly lower impact forces than are required forcommonly used percussion cap primers. As a result, the amount ofdistance that the striker mass 39 has to travel and its required mass isthereby reduced, resulting in a smaller total height (shown as 15 inFIG. 1) of the thermal battery assembly. This choice, however, has thedisadvantage of not using standard and off-the-shelf percussion capprimers, thereby increasing the component and assembly cost of theinertial igniter.

The disclosed inertial igniters are seen to discharge the ignition fireand sparks directly into the thermal battery, FIGS. 4-9, to ignite thepyrotechnic materials 24 within the thermal battery 11 (FIG. 3). As aresult, the additional housing 21 and ignition material 23 shown in FIG.3 can be eliminated, greatly simplifying the resulting thermal batterydesign and manufacture. In addition, the total height 13 and volume ofthe inertial igniter assembly 10 and the total height 15 of the completethermal battery assembly 16 are reduced, thereby reducing the totalvolume that has to be allocated in munitions or the like to house thethermal battery.

The disclosed inertial igniters are shown sealed within their housing,thereby simplifying their storage and increase their shelf life.

FIG. 10 shows the schematic of a cross-section of another embodiment 80.This embodiment is similar to the embodiment shown in FIGS. 4-8, withthe difference that the striker mass 39 (FIGS. 4-8) is replaced with astriker mass 82, with at least one opening passage 81 to guide theignition flame up through the igniter 80 to allow the pyrotechnicmaterials (or the like) of a thermal battery (or the like) positionedabove the igniter 80 (not shown) to be initiated. In addition, the topcap 35 (FIG. 4-8) is preferably eliminated or replaced by a cap 83 withappropriately positioned openings to allow the flames to enter thethermal battery and initiate its pyrotechnic materials. The openings 38(FIG. 5 b) are obviously no longer necessary.

FIG. 11 b shows the schematic of a cross-section of another embodiment90. This embodiment is similar to the embodiment shown in FIGS. 4-8,with the difference that the openings 38 (FIG. 5 b) for the flame toexit the igniter 30 is replaced with side openings 91, FIG. 11 a, toallow the flame to exit from the side of the igniter to initiate thepyrotechnic materials (or the like) of a thermal battery or the like(not shown) that is positioned around the body of the igniter 90.Alternatively, the igniter housing 92 may be eliminated, therebyallowing the generated ignition flames to directly flow to the sides ofthe igniter 90 and initiate the pyrotechnic materials of the thermalbattery or the like.

FIG. 12 shows the schematic of a cross-section of another embodiment100. This embodiment is similar to the embodiment shown in FIGS. 4-8,with the difference that the dead coil section 45 (FIGS. 4-5) isreplaced with a solid, preferably relatively very rigid, cylindricalsection 101. The advantage of using a rigid cylindrical section 101 isthat the balls 42 (FIGS. 4-5) would not tend to cause the individualcoils of the dead coil section 45 to move away from their cylindricallypositioned configuration, thereby increasing the probability that thedead coil section could get stuck by the friction forces due to thepressure exerted by the balls 42 to the interior of the housing 34 (FIG.4) or other similar possible scenarios.

In certain applications, the required reliability levels for initiationof inertial igniters are extremely high. In certain cases, the ignitersshould be designed and manufactured to perform their function withextremely high reliability of nearly 100 percent. Some cases may evenrequire the use of multiple and redundant inertial igniters to obtainnearly 100 percent reliability.

The cost issue is also another important consideration since in smallthermal batteries that have to be initiated by inertial igniters, thecost of inertial igniters may easily be a significant portion of thetotal cost. However, to significantly reduce the cost, inertial ignitershave to be designed with fewer and easy to manufacture parts and be easyto assemble. In addition, the inertial igniters must use mass producedand commercially available parts.

The embodiments of the inertial igniters disclosed below are to providethe aforementioned advantages of the embodiments shown in FIGS. 4-12 andin addition: (1) provide inertial igniters that are significantly morereliable and easy to manufacture than currently available inertialigniters for thermal batteries or the like, particularly for relativelysmall thermal batteries that are used in munitions; (2) provide highlyreliable and at the same time very small inertial igniters that do notoccupy a significant volumes of small thermal batteries; (3) provideinertial igniters that are easy to manufacture and assemble into thermalbatteries; and (4) provide inertial igniters that are readily modifiedto satisfy a wide range of no-fire and all-fire requirements withoutrequiring costly engineering development and manufacturing equipmentchanges.

A need exists for novel miniature inertial igniters for thermalbatteries used in gun fired munitions, that are extremely reliable, lowcost (such as having fewer easy to manufacture parts that are notrequired to be fabricated to very low tolerances), easy to manufactureand assemble, and easy to assemble into a thermal battery (such assimply “drop-in” component during thermal battery assembly). Suchinertial igniters can also be adaptable to a wide range of all-fire andno-fire requirements without requiring a significant amount ofengineering development and testing. Such inertial igniters can also becapable of allowing multiple inertial igniters to be readily packed intothermal batteries as redundant initiators to further increase initiationreliability when such extremely high initiation reliability arewarranted. Such inertial igniters are particularly needed for small andlow power thermal batteries that could be used in fuzing and othersimilar applications. Such inertial igniters must be safe and in generaland in particular they should not initiate if dropped, e.g., from up to5-7 feet onto a concrete floor for certain applications; shouldwithstand high firing accelerations and do not cause damage to thethermal battery, for example up to 20-50,000 Gs or even more; and shouldbe able to be designed to ignite at specified acceleration levels whensubjected to such accelerations for a specified amount of time to matchthe firing acceleration experienced in a gun barrel as compared to highG accelerations experienced during accidental falls which last for veryshort periods of time, for example accelerations of the order of 1000 Gswhen applied for over 5 msec as experienced in a gun as compared to, forexample 2000 G acceleration levels experienced during accidental fallover a concrete floor but which may last only 0.5 msec. Reliability isalso of much concern since the rounds should have a shelf life of up to20 years and could generally be stored at temperatures of sometimes inthe range of −65 to 165 degrees F. This requirement is usually satisfiedbest if the igniter pyrotechnic is in a sealed compartment.

An isometric cross-sectional view of a sixth embodiment of an inertiaigniter is shown in FIG. 13, referred to generally with referencenumeral 200. The full isometric view of the inertial igniter 200 isshown in FIG. 14. The inertial igniter 200 is constructed with igniterbody 201, consisting of a base 202 and at least three posts 203. Thebase 202 and the at least three posts 203, can be integrally formed as asingle piece but may also be constructed as separate pieces and joinedtogether, for example by welding or press fitting or other methodscommonly used in the art. The base 202 of the housing can also beprovided with at least one opening 204 (with a corresponding opening(s)in the thermal battery—not shown) to allow ignited sparks and fire toexit the inertial igniter and enter into the thermal battery positionedunder the inertial igniter 200 upon initiation of the inertial igniterpyrotechnics 215, or percussion cap primer when used in place of thepyrotechnics, similar to the primer 49 in the embodiment 60 shown inFIG. 9. Although illustrated with the opening 204 in the base, theopening (or openings) can alternatively be formed in a side wall as isshown in FIG. 11 a or in the striker mass as is shown in FIG. 10.

The base 202 of the housing may be extended to form a cap for thethermal battery, similar to the cap 36 of the thermal battery 37 shownfor the embodiment 30 in FIGS. 4 and 5.

A striker mass 205 is shown in its locked position in FIG. 13. Thestriker mass 205 is provided with guides for the posts 203, such asvertical surfaces 206 (which may be recessed as shown in the embodiment30 in FIGS. 4 and 5), that are used to engage the corresponding (inner)surfaces of the posts 203 and serve as guides to allow the striker mass205 to ride down along the length of the posts 203 without rotation withan essentially pure up and down translational motion. However, thesurfaces 206 minimize the chances of the striker mass 205 jamming ascompared to the recesses 40. Further, manufacturing precision is reduced(for both the posts 203 and the striker mass 205) when the surfaces 206are used in place of the recesses 40. Consequently, both the strikermass 205 and the inertial igniter structure (which includes the posts203) is easier to produce and less costly when the surfaces 206 are usedin place of the recesses 40.

In its illustrated position in FIGS. 13 and 14, the striker mass 205 islocked in its axial position to the posts 203 by at least one setbacklocking ball 207. The setback locking ball 207 locks the striker mass205 to the posts 203 of the inertial igniter body 201 through the holes208 provided in the posts 203 and a concave portion such as a dimple (orgroove) 209 on the striker mass 205 as shown in FIG. 13. A setbackspring 210, which is preferably in compression, is also provided aroundbut close to the posts 203 as shown in FIGS. 13 and 14. In theconfiguration shown in FIG. 13, the locking balls 207 are prevented frommoving away from their aforementioned locking position by the collar211. The setback spring 210 can be a wave spring with rectangularcross-section. The rectangular cross-section eliminates the need to fixor otherwise retain the striker spring 210 to the collar 211, which isan expensive process; the flat coil spring surfaces minimizes thechances of coils slipping laterally (perpendicular to the direction ofacceleration 218), which can cause jamming and prevent the release ofthe striker mass 205 (preventing the collar to move down enough torelease the locking balls). Furthermore, wave springs generate frictionbetween the waves at contact points along the spring wire, therebyreducing the chances for the collar 211 to rapidly bounce back up andpreventing the striker mass 205 from being released.

The collar 211 is preferably provided with partial guide 212 (“pocket”),which are open on the top as indicated by the numeral 213. The guide 212may be provided only at the location of the locking balls 207 as shownin FIGS. 13 and 14, or may be provided as an internal surface over theentire inner surface of the collar 211 (not shown). The advantage ofproviding local guides 212 is that it results in a significantly largersurface contact between the collar 211 and the outer surfaces of theposts 203, thereby allowing for smoother movement of the collar 211 upand down along the length of the posts 203. In addition, they preventthe collar 211 from rotating relative to the inertial igniter body 201and makes the collar stronger and more massive. The advantage ofproviding a continuous inner recess guiding surface for the lockingballs 207 is that it would require fewer machining processes during thecollar manufacture. Although only one locking ball 207 is illustrated inFIG. 13, more than one can be provided, such as a locking ball 207associated with each post 203. More than one locking ball 207 can alsobe associated with each post 203.

The collar 211 rides up and down on the posts 203 as can be seen inFIGS. 13 and 14, but is biased to stay in its upper most position asshown in FIGS. 13 and 14 by the setback spring 210. The guides 212 areprovided with bottom ends 214, so that when the inertial igniter isassembled as shown in FIGS. 13 and 14, the setback spring 210 which isbiased (preloaded) to push the collar 211 upward away from the igniterbase 201, would “lock” the collar 211 in its uppermost position againstthe locking balls 207. As a result, the assembled inertial igniter 200stays in its assembled state and would not require a top can (similar tothe top cap 35 in the embodiment 30 of FIG. 4) to prevent the collar 211from being pushed up and allowing the locking balls 207 from moving outand releasing the striker mass 205.

In the sixth embodiment, a one part pyrotechnics compound 215 (such aslead styphnate or other similar compound) can be used as shown in FIG.13. The surfaces to which the pyrotechnic compound 215 is attached canbe roughened and/or provided with surface cuts, recesses, projections,or the like and/or treated chemically as commonly done in the art (notshown) to ensure secure attachment of the pyrotechnics material to theapplied surfaces. The use of one part pyrotechnics compound makes themanufacturing and assembly process much simpler and thereby leads tolower inertial igniter cost. The striker mass can be provided with arelatively sharp tip 216 and the igniter base surface 202 is providedwith a protruding tip 217 which is covered with the pyrotechnicscompound 215, such that as the striker mass is released during anall-fire event and is accelerated down (opposite to the arrow 218illustrated in FIG. 13), impact occurs mostly between the surfaces ofthe tips 216 and 217, thereby pinching the pyrotechnics compound 215,thereby providing the means to obtain a reliable initiation of thepyrotechnics compound 215.

Alternatively, a two-part pyrotechnics compound as shown and describedfor the embodiment 30 of FIG. 4 can be used. One part of the two-partpyrotechnics compound 47 (FIG. 4), e.g., potassium chlorate, can beprovided on the interior side of the base 32, such as in a providedrecess (not shown) over the exit holes 38. The second part of thepyrotechnics compound (e.g., red phosphorous) 46 can be provided on thelower surface of the striker mass surface 39 facing the first part ofthe pyrotechnics compound 47, as shown in FIG. 4. In general, variouscombinations of pyrotechnic materials can be used for this purpose. Onecommonly used pyrotechnic material consists of red phosphorous ornano-aluminum, indicated as element 46 in FIG. 4, and is used with anappropriate binder (such as vinyl alcohol acetate resin ornitrocellulose) to firmly adhere to the bottom surface of the strikermass 39. The second component can be potassium chlorate, potassiumnitrate, or potassium perchlorate, indicated as element 47 in FIG. 4,and is used with a binder (such as, but not limited to vinyl alcoholacetate resin or nitrocellulose) to firmly attach the compound to thesurface of the base 32 (such as inside of a recess provided in the base32—not shown) as shown in FIG. 4.

Alternatively, instead of using the pyrotechnics compound 215, FIG. 13,a percussion cap primer or the like (similar to the percussion capprimer 49 used in the embodiment 60 of FIG. 9) can be used. A strikertip (similar to the striker tip 50 shown in FIG. 9 for the embodiment60) can be provided at the tip 216 of the striker mass 205 (not shown)to facilitate initiation upon impact.

The basic operation of the embodiment 200 of the inertial igniter ofFIGS. 13 and 14 is similar to that of embodiment 30 (FIGS. 4-8) aspreviously described. Here again, any non-trivial acceleration in theaxial direction 218 which can cause the collar 211 to overcome theresisting force of the setback spring 210 will initiate and sustain somedownward motion of the collar 211. The force due to the acceleration onthe striker mass 205 is supported at the dimples 209 by the lockingballs 207 which are constrained inside the holes 208 in the posts 203.If an acceleration time in the axial direction 218 imparts a sufficientimpulse to the collar 211 (i.e., if an acceleration time profile isgreater than a predetermined threshold), it will translate down alongthe axis of the assembly until the setback locking balls 205 are nolonger constrained to engage the striker mass 205 to the posts 203. Ifthe acceleration event is not sufficient to provide this motion (i.e.,the acceleration time profile provides less impulse than thepredetermined threshold), the collar 211 will return to its start (top)position under the force of the setback spring 210.

Assuming that the acceleration time profile was at or above thespecified “all-fire” profile, the collar 211 will have translated downpast the locking balls 207, allowing the striker mass 205 to acceleratedown towards the base 202. In such a situation, since the locking balls207 are no longer constrained by the collar 211, the downward force thatthe striker mass 205 has been exerting on the locking balls 207 willforce the locking balls 207 to move outward in the radial direction.Once the locking balls 207 are out of the way of the dimples 209, thedownward motion of the striker mass 205 is impeded only by the elasticforce of the setback spring 210, which is easily overcome by the impulseprovided to the striker mass 205. As a result, the striker mass 205moves downward, causing the tip 216 of the striker mass 205 to strikethe pyrotechnic compound 215 on the surface of the protrusion 217 withthe requisite energy to initiate ignition (similar to the configurationshown for the embodiment 30 in FIG. 8).

In the embodiment 200 of the inertial igniter shown in FIGS. 13 and 14,the setback spring 210 is illustrated as a helical wave spring typefabricated with rectangular cross-sectional wires (such as the onesmanufactured by Smalley Steel Ring Company of Lake Zurich, Ill.). Thisis in contrast with the helical springs with circular wirecross-sections used in the embodiments of FIGS. 4-12. The use of theaforementioned rectangular cross-section wave springs or the like hasthe following significant advantages over helical springs that areconstructed with wires with circular cross-sections. Firstly and mostimportantly, as the spring is compressed and nears its “solid” length,the flat surfaces of the rectangular cross-section wires come in contactand generate minimal lateral forces that would otherwise tend to forceone coil to move laterally relative to the other coils as is usually thecase when the wires are circular in cross-section. Lateral movement ofthe coils can, in general, interfere with the proper operation of theinertial igniter since it could, for example jam a coil to the outerhousing of the inertial igniter (not shown in FIGS. 13 and 14), which isusually desired to house the igniter 200 or the like with minimalclearance to minimize the total volume of the inertial igniter. Inaddition, the laterally moving coils could also jam against the posts203 thereby further interfering with the proper operation of theinertial igniter. The use of the present wave springs with rectangularcross-section eliminates such lateral movement and thereforesignificantly increases the reliability of the inertial igniter and alsosignificantly increases the repeatability of the initiation for aspecified all-fire condition. The second advantage of the use of theaforementioned wave springs with rectangular cross-section, particularlysince the wires can and are usually made thin in thickness andrelatively wide, the solid length of the resulting wave spring can bemade to be significantly less than an equivalent regular helical springwith circular cross-section. As a result, the total height of theresulting inertial igniter can be reduced. Thirdly, since the coil wavesare in contact with each other at certain points along their lengths andas the spring is compressed, the length of each wave is slightlyincreased, therefore during the spring compression the friction forcesat these contact points do a certain amount of work and thereby absorb acertain amount of energy. The presence of such friction forces ensuresthat the firing acceleration and very rapid compression of the springwould to a lesser amount tend to “bounce” the collar 211 back up andthereby increasing the possibility that it would interfere with the exitof the locking balls from the dimples 209 of the striker mass 205 andthe release of the striker mass 205. The above characteristic of thewave springs with rectangular cross-section therefore also significantlyenhances the performance and reliability of the inertial igniter 200while at the same time allowing its height (and total volume) to bereduced.

It is appreciated by those skilled in the art that by varying the massof the striker 205, the mass of the collar 211, the spring rate of thesetback spring 210, the distance that the collar 211 has to traveldownward to release the locking balls 207 and thereby release thestriker mass 205, and the distance between the tip 216 of the strikermass 205 and the pyrotechnic compound 215 (and the tip of the protrusion217), the designer of the disclosed inertial igniter 200 can match theall-fire and no-fire impulse level requirements for various applicationsas well as the safety (delay or dwell action) protection againstaccidental dropping of the inertial igniter and/or the munitions or thelike within which it is assembled.

Briefly, the safety system parameters, i.e., the mass of the collar 211,the spring rate of the setback spring 210 and the dwell stroke (thedistance that the collar 210 has to travel downward to release thelocking balls 207 and thereby release the striker mass 205) must betuned to provide the required actuation performance characteristics.Similarly, to provide the requisite impact energy, the mass of thestriker 205 and the aforementioned separation distance between the tip216 of the striker mass and the pyrotechnic compound 215 (and the tip ofthe protrusion 217) must work together to provide the specified impactenergy to initiate the pyrotechnic compound when subjected to theremaining portion of the prescribed initiation acceleration profileafter the safety system has been actuated.

The striker mass 205 and striker tip 216 may be a monolithic design withthe striking tip 216 being formed, as shown in FIG. 13, or as a bossprotruding from the striker mass, or the striker tip 216 may be aseparate piece, possibly fabricated from a material that issignificantly harder than the striker mass material, and pressed orotherwise permanently fixed to the striker mass. A two-piece designwould be favorable to the need for a striker whose density is differentthan steel, but whose tip would remain hard and tough by attaching asteel ball, hemisphere, or other shape to the striker mass. A monolithicdesign, however, would be generally favorable to manufacturing becauseof the reduction of part quantity and assembly operations.

The use of three or more posts 203 in the embodiment 200 of FIGS. 13 and14 has several significant advantages over the two post designs of theembodiments of FIGS. 4-5. namely, unlike the embodiment 30 of FIGS. 4and 5 in which the striker mass 39 is provided with vertical recesses 40that are used to engage the posts 33 and serve as guides to allow thestriker mass 39 to ride down along the length of the posts 33 withoutrotation, the use of at least three posts 203 in the embodiment 200 ofFIGS. 13 and 14 eliminates the need for the aforementioned verticalrecesses in the striker mass 205. As a result, the chances that thestriker mass 203 gets jammed at the interface between the aforementionedvertical recesses (40 in FIGS. 4 and 5) and the posts (33 in FIGS. 4 and5) are almost entirely eliminated. As a result, the reliability of theinertial igniter is significantly increased. Furthermore, the design ofthe striker mass and the igniter posts and their required manufacturingprocess are significantly simplified and the required manufacturingprecision is also reduced. As a result, the manufacturing cost of thestriker mass as well as the igniter body is significantly reduced. Stillfurther, the contacting surfaces between the striker mass 205 and theposts 203 is increased, thereby allowing for a smoother up and downmovement of the striker mass 205 along the inner surfaces of the posts203.

In the embodiment 200 of FIGS. 13 and 14, following ignition of thepyrotechnics compound 215, the generated flames and sparks are designedto exit downward through the opening 204 to initiate the thermal batterybelow. Alternatively, if the thermal battery is positioned above theinertial igniter 200, the opening 204 can be eliminated and the strikermass could be provided with at least one opening similar to the passage81 of the striker mass 82 of the embodiment 80 of FIG. 10 to guide theignition flame and sparks up through the striker mass 205 to allow thepyrotechnic materials (or the like) of a thermal battery (or the like)positioned above the inertial igniter 200 (not shown) to be initiated.

Alternatively, in a manner similar to that shown in the embodiment 90 ofFIGS. 11 a and 11 b, side ports (openings 91) may be provided to allowthe flame to exit from the side of the igniter to initiate thepyrotechnic materials (or the like) of a thermal battery or the likethat is positioned around the body of the inertial igniter.Alternatively, the igniter housing 261 (FIG. 16) may be eliminated,thereby allowing the generated ignition flames to directly flow to thesides of the igniter 200 and initiate the pyrotechnic materials of thethermal battery or the like.

In FIGS. 13 and 14, the inertial igniter embodiment 200 is shown withoutany outside housing. In many applications, as shown in the schematics ofFIG. 15 a (15 b), the inertial igniter 240 (250) is placed securelyinside the thermal battery 241 (251), either on the top (FIG. 15 a) orbottom (FIG. 15 b) of the thermal battery housing 242 (252). This isparticularly the case for relatively small thermal batteries. In suchthermal battery configurations, since the inertial igniter 240 (250) isinside the hermetically sealed thermal battery 241 (251), there is noneed for a separate housing to be provided for the inertial igniteritself In this assembly configuration, the thermal battery housing 242(252) is provided with a separate compartment 243 (253) for the inertialigniter. The inertial igniter compartment 243 (253) is preferably formedby a member 244 (254) which is fixed to the inner surface of the thermalbattery housing 242 (253), preferably by welding, brazing or very strongadhesives or the like. The separating member 244 (254) is provided withan opening 245 (255) to allow the generated flame and sparks followingthe initiation of the inertial igniter 240 (250) to enter the thermalbattery compartment 246 (256) to activate the thermal battery 241 (251).The separating member 244 (254) and its attachment to the internalsurface of the thermal battery housing 242 (252) must be strong enoughto withstand the forces generated by the firing acceleration.

For larger thermal batteries, a separate compartment (similar to thecompartment 10 over or possibly under the thermal battery hosing 11 asshown in FIG. 1 can be provided above, inside or under the thermalbattery housing for the inertial igniter. An appropriate opening(similar to the opening 12 in FIG. 1) can also be provided to allow theflame and sparks generated as a result of inertial igniter initiation toenter the thermal battery compartment (similar to the compartment 14 inFIG. 1) and activate the thermal battery.

The inertial igniter 200, FIGS. 13 and 14 may also be provided with ahousing 260 as shown in FIG. 16. The housing 260 is preferably one pieceand fixed to the base 202 of the inertial igniter structure 201,preferably by soldering, laser welding or appropriate epoxy adhesive orany other of the commonly used techniques to achieve a sealedcompartment. The housing 260 may also be crimped to the base 202 asshown in FIG. 16 for the inertial igniter embodiment 30. The housing 260may also be crimped to the base 202 at its open end 261, in which casethe base 202 is preferably provided with an appropriate recess 262 toreceive the crimped portion 261 of the housing 260. The housing can besealed at or near the crimped region via one of the commonly usedtechniques such as those described above.

In addition, as shown in FIG. 17, the base 202 of the inertial igniter200 may be extended to form the cap 263, which could be used to form thetop cap of the thermal battery as is shown in FIG. 5 c and identifiedwith the numeral 36 for the inertial igniter embodiment 30.

The inertial igniter embodiment 200 of FIGS. 13 and 14 as provided withthe aforementioned housing 260 and shown in FIG. 16 may also behermetically sealed. To this end, and as shown in FIG. 18, the opening204 can be covered, preferably with a thin membrane 264. The membrane264 can be an integral part of the base 202 and is scorched on itsbottom surface (not seen in the view of FIG. 18) to assist it to breakopen by the pressure generated by the initiation of the pyrotechnicscompound 215 (FIG. 13) upon initiation of the inertial igniter to allowthe generated flame and sparks to enter the thermal battery through theresulting opening.

In another embodiment, more than one inertial igniter, preferablyinertial igniters of the embodiment 200 type are used in a thermalbattery to significantly increase the overall reliability of the thermalbattery initiation under all-fire condition. As a result, if for anyreason one of the inertial igniters fails to initiate or fails toinitiate the thermal battery, then there would be one or more(redundant) inertial igniters to significantly reduce the chances thatthe thermal battery would fail to be activated. The more than oneinertial igniters (preferably of embodiment 200 or any other of theaforementioned embodiments) may in general be assembled in anyappropriate configuration in the thermal battery. For the case of smallthermal batteries, however and if the thermal battery size allows, theinertial igniters are preferably ganged up together in one location, forexample on the top or bottom compartments shown in FIGS. 15 a and 15 bor in the compartment 10 shown in FIG. 1, to minimize the total volumeand size occupied by the inertial igniters. For example, when threeinertial igniters of the embodiment 200 are to be assembled within athermal battery, for example of the type shown in FIG. 15 a, assumingthat the amount of space available in the compartment 243 isappropriate, the three inertial igniters 200 may be ganged up inside thecompartment 243 as shown in the top view of FIG. 19 (the top cap isremoved to show the inertial igniters 200 inside the compartment 243).

When more than one inertial igniter 200 (or of other embodiment types)are ganged up in a compartment similar to that of 243 as shown in FIG.19, the body 201 of two or more of the inertial igniters 200 may beintegral. For example, the bodies 201 of the three inertial igniters 200shown in FIG. 19 may be integral as shown in the top and isometric viewsof FIGS. 20 a and 20 b, respectively, and identified with referencenumeral 265.

In certain applications, it is desired that the inertial igniters gangedup in a compartment such as 243 as shown in FIG. 19 be separated by awall so that their operations and/or failure (such as flying piecesfollowing initiation or break up of one igniter) would not interferewith the operation of the remaining inertial igniters. In such cases,the inertial igniter bodies (such as the bodies 201 of the inertialigniters 200, FIGS. 13 and 19) and the separation walls 206 between atleast two of the inertial igniters may be integral as shown in theisometric and top views of FIGS. 21 a and 21 b, respectively, andindicated by reference numeral 266. In the drawings of FIGS. 21 a and 21b, all three inertial igniters 200 are intended to be separated fromeach other by the walls 267.

The present inertial igniters are designed such that when ganged up asshown in FIGS. 20 a or FIG. 21 a, their integral bodies 201 can bereadily machined, for example from a solid rod, using commonly used CNCmachining centers or the like.

In the above embodiments, the disclosed devices are intended to actuate,i.e., release their striker mass (element 39 in the embodiment of FIGS.4 and 5 and element 205 in the embodiments of FIGS. 13 and 14) inresponse to an all-fire setback acceleration event in the direction ofthe indicated arrows and accelerate the striker mass downwards to impactthe provided pyrotechnics materials causing them to ignite. The samemechanism used for the release of the striker mass due to an all-fireacceleration event (usually a prescribed acceleration level with aprescribed duration, i.e., a prescribed impulse threshold) can be usedto provide the means of opening or closing or both of at least oneelectrical circuit, i.e., act as a G-switch, that is actuated only if itis subjected to an all-fire acceleration profile, while staying inactiveduring all no-fire conditions, even if the acceleration level is higherthan the all-fire acceleration level but significantly shorter induration. As a result, this novel G-switch device would satisfy allno-fire (safety) requirements of the device in which it is used whileactivating in the prescribed all-fire condition.

G-switches also have numerous other non-munitions applications. Forexample, G-switches can be used to detect events such as impacts, falls,structural failure, explosions, etc., and open or close electricalcircuits to initiate prescribed actions.

It is also appreciated by those skilled in the art that more than oneG-switch may be employed with each configured to activate at a differentimpulse threshold level so that different impulse levels can also bedetected. The G-switches may also be directed in more than oneindependent direction, for example in three independent directions, todetect and activate impulse threshold levels in any arbitrary direction.

The need to differentiate accidental (all no-fire conditions inmunitions) and all-fire acceleration events by the resulting impulselevel of the event necessitates the employment of a safety mechanismwhich is capable of allowing G-switch activation only during high(prescribed) total impulse levels. The safety mechanism can be thoughtof as a mechanical delay mechanism that begins the time delay processonce a prescribed acceleration level is reached, after which a separateswitching mechanism is actuated to provide the desired electric circuitopening or closing switching action. Such impulse-based G-switch thatcombine such safety mechanisms with electrical circuit opening/closingswitching mechanisms and their alternative embodiments are describedherein together with alternative methods of their design, particularlyas modular designs that can be readily assembled to varyingrequirements.

The disclosed impulse-based G-switches function in a manner similar tothe disclosed inertia-based igniters. They similarly comprise of twobasic mechanisms so that together they provide the aforementionedmechanical safety (delay mechanism) and the switching action to open orclose electrical circuits. The function of the safety system is toprevent activation of the switching mechanism until the prescribedacceleration time profile actuates the safety mechanism and releases theswitching mechanism, thereby allowing it to undergo its actuation motionto open or close the electrical circuit by connecting or disconnectingelectrical contacts.

The basic design of such G-switches using the design and functionalitiesof the disclosed inertial igniter embodiments is herein described usingthe inertial igniter embodiment of FIG. 16. However, it is appreciatedby those skilled in the art that the inertial igniter embodiments ofFIGS. 4-14, 16-18 and multiple unit design embodiments of FIGS. 19-21may also be similarly modified to G-switches as will be described belowfor the embodiment of FIG. 16.

The schematic of a G-switch embodiment 300 is shown in FIG. 22. Thebasic design of the G-switch 300 is similar to the variation of FIG. 16of the inertial igniter embodiment of FIGS. 13-14, except that itspyrotechnic material is removed and electrical switching contacts andrelated elements are provided to convert the inertial igniter into aG-switch for opening or closing electrical circuits.

It is noted that in the schematic of the embodiment 300 of FIG. 22 (aswell as in the embodiments of FIGS. 16-18) a helical spring 301 is shownfor clarity of the illustration. However, in the G-switches (as well asthe embodiments of FIGS. 16-18), the setback spring 301 can be a wavespring with rectangular cross-section or the like as shown in FIGS. 13and 14 and indicated by the numeral 210. It is appreciated by thoseskilled in the art that the rectangular cross-section eliminates theneed to fix or otherwise retain the striker spring 210 to the collar 211since it provides multiple points of support to the collar 211. The flatcoil spring surfaces also minimizes the chances of coils slippinglaterally (perpendicular to the direction of acceleration 218, FIG. 13),which can cause jamming and prevent the release of the striker mass 205(preventing the collar to move down enough to release the lockingballs). Furthermore, wave springs generate friction between the waves atcontact points along the spring wire, thereby reducing the chances forthe collar 211 to rapidly bounce back up and preventing the striker mass205 from being released.

In the G-switch embodiment 300 shown in FIG. 22, an element 302 which isconstructed of an electrically non-conductive material is fixed to thebase 201 of the device. The element 302 is provided with twoelectrically conductive elements 303 and 304 with contact ends 305 and306, respectively. The electrically conductive elements 303 and 304 maybe provided with the extended ends 307 and 308, respectively, to formcontact “pins” for direct insertion into provided holes in a circuitboard or may alternatively be provided with wires 309 and 310 forconnection to appropriate circuit junctions, in which case, the wires309 and 310 are preferably routed out from the sides of the G-switch 300(not shown). Previously described (striker) element 205 is provided witha flexible strip of electrically conductive material 311 which is fixedto the bottom surface of the element 205 (preferably soldered orattached with fasteners 312) but can also be formed integrally with thestriker element 205.

The operation of the G-switch embodiment 300 of FIG. 22 is very similarto that of the inertial igniter of FIGS. 13 and 14. Here again and aswas described for the inertial igniter of FIGS. 13 and 14, anynon-trivial acceleration in the axial direction 218 (313 in FIG. 22)which can cause the collar 211 to overcome the resisting force of thesetback spring 210 (301 in FIG. 22) will initiate and sustain somedownward motion of the collar 211. If the device is subjected to anacceleration event in the direction of the arrow 313 (218 in FIG. 13)that imparts sufficient impulse corresponding to the prescribed all-firecondition (i.e., if an acceleration time profile is greater than apredetermined threshold) to the collar 211, it will translate down alongthe axis of the assembly until the setback locking balls 207 are nolonger constrained to engage the striker mass 205 to the posts 203. Ifthe acceleration event is not sufficient to provide this motion (i.e.,the acceleration time profile provides less impulse than thepredetermined threshold), the collar 211 will return to its start (top)position under the force of the setback spring 210. If the accelerationtime profile was at or above the specified “all-fire” profile, thecollar 211 will have translated down past the locking balls 207,allowing the striker mass 205 to accelerate down towards the base 202.

Now as can be seen in FIG. 22, as the element 205 is released and movesdownward towards the base 202 of the device, it would cause the flexibleelectrically conductive strip 311 to come into contact with the contacts305 and 306, thereby causing the circuit through the wires 309 and 310to close.

It is appreciated by those skilled in the art that after the flexiblestrip 311 has come into contact with the contacts 305 and 306 andthereby causing the circuit through the wires 309 and 310 to close, theelement 205 may bounce back, thereby causing the contact being lost. Infact, the contacts, i.e., the closing of the circuit may beintermittently lost several times during the all-fire event and evenafterwards due to vibratory and oscillatory motions of the munitions orother objects to which the G-switch 300, FIG. 22, is attached.

In certain applications, the G-switch is required only to produce aninitial pulse to perform its required function. For such applications,the G-switch embodiment of FIG. 22 is configured to provide such pulse.In other applications, the G-switch may be required to keep theelectrical circuit close, i.e., keep the flexible strip 311 and thecontacts 305 and 306 in contact following initial contact, even if theG-switch is subjected to certain levels of vibratory and other similartypes of motions. To achieve this goal, the element 205 can be providedwith a biasing spring to ensure that the flexible electricallyconductive strip 311 stays in contact with the contacts 305 and 306 asshown in the embodiment 320 of FIG. 23.

In the G-switch embodiment 320 of FIG. 23, the biasing spring can be acompressively preloaded helical spring 314 or a wave spring similar tothe wave spring 210 shown in FIG. 13, or the like which is positioned ina pocket 315 that is provided in the element 205 as shown in theschematic of FIG. 23. Here the compressively preloaded spring 314 ispositioned in the pocket 315 and preloaded against the inside surface ofthe top portion of the G-switch housing 260 as shown in FIG. 23. Thespring 314 can be provided with enough biasing compressive preloadingthat would provide an appropriate amount of compressive force to theelement 205 after the G-switch activation and when the flexible strip311 has come into contact with the contacts 305 and 306 such that theywould stay in contact and keep the electrical circuit closed afterinitial establishment of the contact and as the device is subjected topossible shock loading and/or vibratory and other similar motions.

In an alternative embodiment of the G-switch 320 of FIG. 23, the springelement 314 can be preloaded in tension instead of compression. Thespring 314 can also be fixed on one end to the top of the G-switchhousing 260 and is fixed on the other end to the element 205. Then whenthe G-switch 320 is subjected to an all-fire acceleration in thedirection of arrow 313, the element 205 is released as was previouslydescribed and is accelerated downward towards the base 202 of thedevice, eventually causing the flexible electrically conductive strip311 to come into contact with the contacts 305 and 306, thereby causingthe circuit through the wires 309 and 310 to close. During this process,the spring element 314 is subjected to further tensile force. The springrate and the tensile preloading of the spring element 314 and the massof the element 205 are selected such that the force generated by theall-fire acceleration in the direction of the arrow 313 acting on theinertia of the element 205 is larger than the tensile force of thespring acting on the element 205. Then once the all-fire accelerationhas ended or dropped below a prescribed threshold, the tensile force ofthe spring element 314 will pull the element 205 up, thereby causingcontact between the flexible electrically conductive strip 311 and thecontacts 305 and 306 to be lost, thereby causing the connected closedelectrical circuit to become opened. This alternative embodiment of theG-switch 320 of FIG. 23 would essentially keep the connected circuitclosed only during (mostly a portion) of the prescribed all-fire event,providing a pulse-like effect.

In the G-switch embodiments of FIGS. 22 and 23, the G-switch isconfigured as a “normally open” type of switch, i.e., it is used toclose an electrical circuit upon activation, for example, upon detectionof all-fire condition in munitions applications. It is, however,appreciated by those skilled in the art that the “normally open”G-switch embodiments 300 and 320 of FIGS. 22 and 23, respectively, canbe readily modified to open an already closed electrical circuit uponactivation, i.e., to be modified into “normally closed” G-switches.

The G-switch 300 and 320 of FIGS. 22 and 23, respectively, can also bereadily modified to provide a “normally close” switching configuration.As an example, the contact components of the G-switch 320 may bemodified to those of the embodiment 350 shown in the schematic of FIG.24. In the embodiment 350 of the “normally closed” G-switch all itscomponents are the same as those of the embodiment 320 of FIG. 23,except the following electrical circuit closing elements. The “normallyclosed” G-switch 350 is provided with two electrically conductiveflexible contact elements 316 and 317, which are fixed to theelectrically non-conductive member 302, which is fixed to the base 202of the G-switch 350. The electrically conductive flexible contactelements 316 and 317 may be provided with the extended ends 321 and 322,respectively, to form contact “pins” for direct insertion into providedholes in a circuit board or may alternatively be provided with wires 323and 324 for connection to appropriate circuit junctions, in which case,the wires 323 and 324 can be routed out from the sides of the G-switch300 (not shown).

The flexible contact elements 316 and 317 are provided with contactpoints 318 and 319, respectively, which are normally in contact, therebycausing the wires 323 and 324 to close the electrical circuit to whichthey are connected to. The element 205 is provided with a non-conductiveelement 325 as shown in FIG. 24. As it was described for the embodimentsof FIGS. 22 and 23, when the G-switch 350 is subjected to an all-fireacceleration in the direction of arrow 313, the element 205 is releasedand is accelerated downward. As the non-conductive element 325 reachesthe contact points 318 and 319, the force of the acceleration acting onthe inertia of the element 205 and/or the force provided by thecompressively preloaded spring 314 causes the element 325 to be insertedbetween the contact points 318 and 319, thereby rendering their contactsopen and thereby opening the aforementioned electrical circuit to whichthe wires 323 and 324 are connected.

In an alternative embodiment of the G-switch 350 of FIG. 24, the springelement 314 can be preloaded in tension instead of compression. Thespring 314 is also fixed on one end to the top of the G-switch housing260 and is fixed on the other end to the element 205. Then when theG-switch 350 is subjected to an all-fire acceleration in the directionof arrow 313, the element 205 is released as was previously describedand is accelerated downward towards the base 202 of the device. As thenon-conductive element 325 reaches the contact points 318 and 319, theforce of the said acceleration acting on the inertia of the element 205causes the element 325 to be inserted between the contact points 318 and319, thereby rendering their contacts open and thereby opening theaforementioned electrical circuit to which the wires 323 and 324 areconnected. During this process, the spring element 314 is subjected tofurther tensile force. The spring rate and the tensile preloading of thespring element 314 and the mass of the element 205 are selected suchthat the force generated by the all-fire acceleration in the directionof the arrow 313 acting on the inertia of the element 205 is larger thanthe tensile force of the spring acting on the element 205 and is enoughto insert the element 325 between the contact points 318 and 319. Thenonce the said all-fire acceleration has ended or dropped below aprescribed threshold, the tensile force of the spring element 314 willpull the element 205 and the non-conductive element 325 up, therebycausing contact between the contact points 318 and 319 to bere-established, thereby causing the opened electrical circuit to becomeclosed. This alternative embodiment of the G-switch 350 of FIG. 24 wouldessentially keep the connected circuit open only during (mostly aportion) of the prescribed all-fire event, providing a pulse-likeeffect.

In the G-switch embodiments of FIGS. 22-24, only one “normally open” or“normally closed” switching contact are provided. It is, however,appreciated by those skilled in the art that more than one such“normally open” or “normally closed” switching contacts or a combinationof at least one “normally open” and “normally closed” may be provided ineach of the G-switch embodiments of FIGS. 22-24 to open or close severalelectrical switches when the device is subjected to previously describedprescribed all-fire event.

In the embodiments of FIGS. 22-24, the element 205 is released whenall-fire acceleration profile threshold is experienced by the G-switch.The element 205 is then moved down due to the all-fire accelerationand/or a preloaded compressive spring element, thereby causing certainelectrical contacts to be bridged by a conducting element or separatedby a non-conducting element to open or close certain electricalcircuit(s). The G-switches may, however, be configured such that thereleased element (element 205 in the embodiments of FIGS. 22-24) areforced to move up (as shown in FIGS. 22-24) instead and thereby causingelectrical circuits to similarly open or closed as described below.

The schematic of such a G-switch embodiment 400 is shown in FIG. 25. Theconfiguration of the G-switch 400 is similar to the G-switch embodiment300 of FIG. 22 except for the differences that will be described.Similar to the G-switch embodiment 300 of FIG. 22, the G-switch 400 isprovided with the element 302, which is constructed of an electricallynon-conductive material is fixed to the base 201 of the device. Theelement 302 is similarly provided with two electrically conductiveelements 303 and 304 with contact ends 305 and 306, respectively. Theelectrically conductive elements 303 and 304 may be provided with theextended ends 307 and 308, respectively, to form contact “pins” fordirect insertion into provided holes in a circuit board or mayalternatively be provided with wires 309 and 310 for connection toappropriate circuit junctions, in which case, the wires 309 and 310 canbe routed out from the sides of the G-switch.

A difference between the G-switch embodiment 300 of FIG. 22 and G-switchembodiment 400 of FIG. 25 is that the posts 402 (203 in the embodimentof FIG. 22) are sized such that the element 403 (205 in the embodimentof FIG. 22) can slide up along the posts 402, as was previouslydescribed for the downward motion of the element 205 for the embodimentsof FIGS. 22-24, following its release due to downward motion of thecollar 211 when the G-switch is subjected to an acceleration profilecorresponding to the prescribed all-fire condition. The element 403(“striker” element 205 in the embodiment of FIG. 22) is similarlyprovided with a flexible strip of electrically conductive material 404(311 in the embodiment of FIG. 22) which is fixed to the bottom surfaceof the element 403 (such as being soldered or attached with fasteners405). In its pre-release configuration shown in FIG. 25, the element 403is positioned such that the flexible strip of electrically conductivematerial 404 is pushed against the contacts 305 and 306, such as beingbiased against the contacts 305 and 306 due to a flexible strip ofelectrically conductive material 404, thereby keeping the electricalcircuit connected to the “pins” 307 and 308 (or wires 309 and 310)closed. The element 403 is also provided with a tensile spring 407,which is attached on one end to the element 403 and on the other end tothe inner surface of the top portion of the G-switch housing 409. Theelement 403 can be provided with a pocket 408 to allow the use of arelatively long tensile spring. The tensile spring can be preloaded intension.

Here again and as was described for the inertial igniter of FIGS. 13 and14, any non-trivial acceleration in the axial direction of the arrow 218(406 in FIG. 25) which can cause the collar 211 to overcome theresisting force of the setback spring 210 (401 in FIG. 25) will initiateand sustain some downward motion of the collar 211. If the device issubjected to an acceleration event in the direction of the arrow 406(218 in FIG. 13) that imparts sufficient impulse corresponding to theprescribed all-fire condition (i.e., if an acceleration time profileprovides an impulse that is greater than a predetermined threshold) tothe collar 211, it will translate down along the axis of the assemblyuntil the setback locking balls 207 are no longer constrained to engagethe element 403 (“striker” mass 205 in FIG. 22) to the posts 402 (203 inFIG. 22). If the acceleration event is not sufficient to provide thismotion (i.e., the acceleration time profile provides less impulse thanthe predetermined threshold), the collar 211 will return to its start(top) position under the force of the setback spring 402 (301 and 210 inFIGS. 22 and 13, respectively). If the acceleration time profile was ator above the specified “all-fire” profile, the collar 211 will havetranslated down past the locking balls 207, allowing the element 403(corresponding to striker mass 205 in FIGS. 13 and 22) to be releasedand free to slide along the posts 402. At this time, the tensile spring407 which is preloaded in tension will force the element 403 to slide upalong the posts 402, thereby causing the contact between the flexiblestrip of electrically conductive material 404 and the contact points 305and 306 to be lost, and thereby the electrical circuit to which G-switchwires 309 and 310 (or “pins” 307 and 308) is attached become opened.

It is noted that in the schematic of the embodiment 400 of FIG. 25helical springs 401 and 407 are shown for clarity of the illustration.However, in the G-switches, the compressive setback spring 401 and thetensile spring 407 can be wave springs with rectangular cross-section orthe like as shown in FIGS. 13 and 14 for the setback spring 401 andindicated by the numeral 210 for the reasons set forth above.

As was previously indicated for the embodiment 300 of FIG. 22, when theG-switch 300 is subjected to the aforementioned all-fire setbackcondition and the element 205 is released and is accelerated downward,after the said flexible strip 311 has come into contact with thecontacts 305 and 306 and thereby causing the circuit through the wires309 and 310 to close, the element 205 may bounce back, thereby causingthe said contact being lost. In fact, the contacts, i.e., the closing ofthe circuit may be intermittently lost several times during the all-fireevent and even afterwards due to vibratory and oscillatory motions ofthe munitions or other objects to which the G-switch 300 is attached. Itis, however, appreciated by those skilled in the art that for the caseof the G-switch 400 of FIG. 25, the tensile spring 407 can be providedwith high enough tensile preloading so that once the collar 211 hasmoved down and released the element 403, the force generated by theacceleration in the direction of the arrow 406 acting on the inertial ofthe element 403 is less than the said tensile preloading of the tensilespring 407. As a result, once the contact between the electricallyconductive flexible strip 404 and the contact points 305 and 306 islost, it would not be intermittently established afterwards.

In an alternative embodiment of the G-switch 400 of FIG. 25, the springelement 407 is replaced by a preloaded compressive spring that can bepositioned between the upper surface 410 of the base 202 and the lowersurface 411 of the element 403 (not shown). With this alternativedesign, the pocket 408 in the element 403 is no longer needed and theelement 403 and the entire G-switch can be made significantly smaller.

In an alternative embodiment of the G-switch 400 of FIG. 25 shown inFIG. 26 and indicated as embodiment 420, the G-switch 400 can bemodified for closing electrical circuits when subjected toaforementioned all-fire conditions. Similar to the embodiment 320 ofFIG. 24, the embodiment 400 of FIG. 25 can be modified into a G-switchfor opening an electrical circuit when subjected to the aforementionedall-fire condition. To this end, the element 302 is similarly providedwith two electrically conductive elements 421 and 422 with flexiblecontact ends 423 and 424 (318 and 319 in the embodiment of FIG. 24),respectively. The electrically conductive elements 421 and 422 may besimilarly provided with the extended ends 425 and 426, respectively, toform contact “pins” for direct insertion into provided holes in acircuit board or may alternatively be provided with wires 427 and 428,respectively, for connection to appropriate circuit junctions, in whichcase, the wires 427 and 428 can be routed out from the sides of theG-switch.

The element 403 is provided with a non-conductive element 429 as shownin FIG. 26. As it is shown in the schematic of FIG. 26, thenon-conductive element 429 is positioned between the flexible contactends 423 and 424, thereby causing them to be flexibly bend back (fromthe positions shown for the contacts 318 and 319 for the embodiment 320of FIG. 24), and preventing contact between the flexible contact ends423 and 424 to be established. Then, as it was described for theembodiment 400 of FIG. 25, when the G-switch 420 is subjected to anall-fire acceleration in the direction of arrow 406, the element 403 isreleased and as the acceleration in the direction of the arrow 406 dropsbelow certain prescribed level, the element 403 is pulled upwards awayfrom the base 202 of the G-switch by the preloaded tensile spring 407.The non-conductive element 429 is thereby pulled up and out of contactbetween the flexible contact ends 423 and 424, thereby allowing theflexible contact ends 423 and 424 which are elastically biased towardseach other to come into contact and close the electrical circuit towhich the G-switch (wires 427 and 428 or “pins” 425 and 426) isconnected.

In an alternative embodiment of the G-switch 420 of FIG. 26, the springelement 407 is replaced by a preloaded compressive spring as wasdescribed for the embodiment 400 of FIG. 25. The compressive spring canbe positioned between the upper surface 410 of the base 202 and thelower surface 411 of the element 403 (not shown). With this alternativedesign, the pocket 408 in the element 403 is no longer needed and theelement 403 and the entire G-switch can be made significantly smaller.

In the G-switch embodiments of FIGS. 25-26, only one “normally open” or“normally closed” switching contact are provided. It is, however,appreciated by those skilled in the art that more than one such“normally open” or “normally closed” switching contacts or a combinationof at least one “normally open” and “normally closed” may be provided ineach of the G-switch embodiments of FIGS. 25-26 to open or close severalelectrical switches when the device is subjected to previously describedprescribed all-fire event.

In the G-switch embodiments of FIGS. 22-26, the flexible electricallyconductive elements (311 in FIGS. 22 and 23 and 404 in FIG. 25) used toclose an electrical circuit by coming into contact with contact points305 and 306 and the non-conductive elements (325 in FIGS. 24 and 429 inFIG. 26) used to open an electrical circuit by separating flexiblecontact ends 318 and 319 in FIG. 24 and flexible contact ends 423 and424 in FIG. 26 by being inserted between the said flexible contact endsare attached to the element 205 (in FIGS. 22-24) and element 403 (inFIGS. 25 and 26). The elements 205 and 403 are then locked to the posts203 (in FIGS. 22-24) and 402 (in FIGS. 25 and 26) by the balls 207, andreleased when the aforementioned all-fire condition (impulse levelcorresponding to a prescribed acceleration profile level) occurs and thecollar 211 is displaced down and releases the locking balls 207. Assuch, said elements 205 and 403 serve as “intermediate” elements towhich the flexible electrically conductive elements (311 in FIGS. 22 and23 and 404 in FIG. 25) and non-conductive elements (325 in FIGS. 24 and429 in FIG. 26) are fixedly attached. In alternative embodiments of theembodiments of FIGS. 22-26, the “intermediate” element is integratedwith the flexible electrically conductive elements (311 in FIGS. 22 and23 and 404 in FIG. 25) and non-conductive elements (325 in FIGS. 24 and429 in FIG. 26).

Such an integrated element 430 for the embodiments of FIGS. 24 and 26 isshown in FIG. 27. In this design, the tip 432 (325 in FIGS. 24 and 429in FIG. 26) is integrated with the element body 431. The element 430 isconstructed with an electrically non-conductive material such as a hardplastic, preferably produced by injection molding. A metal insert may beused in the molding of the element 430 (except in its tip 432) if itsmass is required to be increased due to relatively low all-firegenerated impulse level. Such a design will significantly reduce thecost of producing such G-switches.

For the case of the embodiments of FIGS. 22, 23 and 25, the flexibleelectrically conductive elements (311 in FIGS. 22 and 23 and 404 in FIG.25) may be similarly molded as an insert 434 into the (preferably hardplastic) body 433 of the integrated element 435 (element 205 in FIGS.22-24 and element 403 in FIGS. 25 and 26) as shown in FIG. 28.Alternatively, the elements 205 in the embodiments of FIGS. 22 and 23and the element 403 in the embodiment of FIG. 25 may be constructed withan electrically conductive material, preferably corrosion resistantmetals such brass or stainless steel, while the electrical contacts 305and 306 are constructed with flexibility, preferably in bending as iscommonly done in battery or the like contacts such as contact elements436 and 437 shown in FIG. 29. The two electrically conductive elements303 and 304 to which the flexible contact elements 436 and 437 areattached and the extended ends 307 and 308 can be inserts in a moldingof the electrically non-conductive element 302 (such as a hardelectrically non-conductive plastic material used in the element 302molding) as shown in FIG. 29.

It is noted that the G-switch embodiments of FIGS. 22-26 are shown to beconstructed by the modification of the inertial igniter embodiment ofFIGS. 13-14 as shown in the basic a cross-sectional view of FIG. 16. Itis, however, appreciated by those skilled in the art that any one of theinertial igniter embodiments may be similarly converted to a G-switchfor opening or closing one or more electrical circuits when subjected toa prescribed all-fire condition as was previously described.

It is also appreciated by those skilled in the art that two or more ofsuch G-switches may also be “ganged up” similar to the inertial ignitersshown in FIGS. 19-21 for one or more of the following purposes:

-   -   To increase reliability by providing more than one G-switch to        open or close an electrical circuit;    -   To provide multiple G-switches, each of which may be used to        open or close an electrical circuit upon a different level of        experienced impulse level, i.e., upon experiencing different        acceleration-time profiles. As such, different imparted impulse        levels can be detected by the device using the said G-switches;    -   To provide the means to open or close multiple electrical        circuits. This option would also allow the use of several        G-switches each with one or a limited number of electrical        circuit opening or closing contacts.

While there has been shown and described what is considered to bepreferred embodiments of the invention, it will, of course, beunderstood that various modifications and changes in form or detailcould readily be made without departing from the spirit of theinvention. It is therefore intended that the invention be not limited tothe exact forms described and illustrated, but should be constructed tocover all modifications that may fall within the scope of the appendedclaims.

What is claimed is:
 1. A G-switch comprising: a body having a base andtwo or more posts extending from the base, each of the two or more postshaving a hole; at least one locking ball corresponding to each of thetwo or more posts, wherein a first portion of the locking balls aredisposed in the hole; a striker mass movably disposed relative to thetwo or more posts and having a surface corresponding to each of the twoor more posts, the movement of the striker mass being guided by thesurfaces, the striker mass further having a concave portioncorresponding to each of the locking balls, wherein a second portion ofeach locking ball is disposed in a corresponding concave portion forretaining the striker mass relative to the two or more posts; a collarmovable relative to the two or more posts; a biasing element for biasingthe collar in a first position which retains the locking balls withinthe concave portions, the biasing element permitting movement of thecollar to a second position in which the locking balls can be releasedfrom the concave portions to release the striker mass relative to thetwo or more posts upon a predetermined acceleration profile experiencedby the body; a member disposed on the striker mass; and first and secondelectrically conductive contacts disposed on a portion of the body;wherein the first member one of opening or closing an electrical circuitbetween the first and second contacts upon release of the striker mass.2. The G-switch of claim 1, wherein the two or more posts comprise threeposts.
 3. The G-switch of claim 1, wherein the portion of the bodycomprises the base, the base having a non-conductive material, the firstand second contacts being disposed in the non-conductive material. 4.The G-switch of claim 3, wherein each of the first and second contactscomprise a contact head and an extended end connected to the contacthead, the extended end being disposed in the non-conductive material. 5.The G-switch of claim 3, wherein the contact head is a flexible member.6. The G-switch of claim 1, wherein the member comprises an electricallyconductive third contact to close the electrical circuit between thefirst and second contacts upon release of the striker mass.
 7. TheG-switch of claim 6, wherein the third contact is a flexible member. 8.The G-switch of claim 6, further comprising a contact biasing elementfor biasing the third contact to stay in electrical contact with thefirst and second contacts after release of the striker mass.
 9. TheG-switch of claim 1, wherein the member comprises an electricallynon-conductive member to open the electrical circuit between the firstand second contacts upon release of the striker mass.
 10. The G-switchof claim 9, further comprising a contact biasing element for biasing theelectrically non-conductive member to maintain the first and secondcontacts open after release of the striker mass.
 11. The G-switch ofclaim 1, further comprising a striker mass biasing element for biasingthe striker mass away from the second and third contacts to one of openor close the electrical circuit upon release of the striker mass. 12.The G-switch of claim 6, wherein the striker mass comprises anon-conductive material body and the electrically conductive thirdcontact is insert molded into the non-conductive material body.
 13. TheG-switch of claim 9, wherein the striker mass comprises a non-conductivematerial body and the electrically non-conductive member is integrallyformed with the non-conductive material body.